1. Technical Field of the Invention
The present invention relates generally to an ultrasonic probe which is used in, for example, medical applications to radiate an ultrasonic wave for inspecting the interior of a patient""s body noninvasively, and more particularly to an improved structure of a scan mechanism of an ultrasonic probe designed to rotate a piezoelectric element emitting the ultrasonic wave.
2. Background Art
Japanese Patent First Publication No. 5-337108 teaches a scan mechanism for an ultrasonic probe. The scan mechanism includes a rotor having a piezoelectric element installed thereon and two electric motors one of which rotates the piezoelectric element about a first axis and other of which swings the piezoelectric element about a second axis perpendicular to the first axis.
The scan mechanism is, however, complex and bulky in structure and encounters the drawback in that it is difficult to use the ultrasonic probe in a small cavity of a person""s body, for example.
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide a simple, lightweight, and inexpensive structure of a scan mechanism of an ultrasonic probe designed to rotate a piezoelectric element emitting an ultrasonic wave.
According to one aspect of the invention, there is provided an ultrasonic probe which comprises: (a) a piezoelectric element emitting an ultrasonic wave and receiving an echo thereof, the piezoelectric element converting the echo into an electric signal; (b) a holding member holding the piezoelectric element; (c) a rotating mechanism rotating the holding member about a first axis; (d) a rotary base supporting the rotating mechanism; (e) a chassis supporting the rotary base so as to allow the rotary base to swing about a second axis extending in a direction different from the first axis; and (f) a swinging mechanism swinging the rotary base.
In the preferred mode of the invention, the rotating mechanism includes a holding member angular position measuring encoder designed to measure an angular position of the holding member.
The holding member angular position measuring encoder may include a first encoder unit and a second encoder unit each of which is made of a magnetic member and a magnetoresistive element. The first encoder unit is designed to measure a change in angular position of the holding member by rotation about the first axis. The second encoder unit is designed to measure a preselected reference angular position of the holding member.
The rotating mechanism includes a holding member rotating electric motor rotating the holding member made of a rotary cylinder, a conductive cylinder arranged in alignment of a central axis with a central axis of the rotary cylinder, and a conductive brush installed on the rotary base in contact with the conductive cylinder.
The rotating mechanism may alternatively include a holding member rotating electric motor rotating the holding member made of a rotary cylinder, a first coil installed on the rotary cylinder, and a second coil installed on the rotary base so as to face the first coil. The first coil is responsive to a change in magnetic flux of the second coil to produce an electric signal for energizing the piezoelectric element.
The swinging mechanism includes a rotary base swinging electric motor, an motor angular position measuring encoder measuring an angular position of the rotary base swinging electric motor, and a gear train transmitting output torque of the rotary base swinging electric motor to the rotary base to swing the rotary base.
The swinging mechanism may alternatively include a voice coil motor and a rotary base angular position measuring encoder which measures an angular position of the rotary base. The voice coil motor is implemented by a magnet installed on one of the rotary base and the chassis and an electric coil installed on the other of the rotary base and the chassis.
A holding mechanism may also be provided which is designed to hold the rotary base on the chassis.
A second piezoelectric element may further be installed on the holding member which produces an ultrasonic wave having the same frequency of that produced by the piezoelectric element.
The second piezoelectric element may alternatively be designed to produce an ultrasonic wave having a frequency different from that produced by the piezoelectric element.
A magnetoresistive element may also be provided which is responsive to a change in magnetic flux produced by the magnetic member of the second encoder to provide a signal indicative of a neutral position of the holding member in swinging motion of the holding member.
An array of magnetoresistive elements may also be installed on the chassis. Each of the magnetoresistive elements is responsive to a change in magnetic flux produced by the magnetic member of the second encoder to provide a signal indicative thereof.